1. Field of the Invention
The present invention relates to an exhaust gas cleaning system for a multi-cylinder internal combustion engine, particularly for motorcycles, adapted to supply the exhaust system of the internal combustion engine with secondary air to promote oxidation of unburnt noxious components in the exhaust gas flowing through the exhaust system.
2. Description of the Prior Art
An exhaust gas cleaning system of the above type is known comprising a secondary air supplying system connected to the exhaust system of an internal combustion engine, the secondary air supplying system being equipped at an intermediate portion with a reed valve device adapted to be opened and closed by the pulsating exhaust gas pressure to introduce the secondary air into the exhaust system for cleaning the exhaust gas.
The above-mentioned reed valve device can operate without requiring any specific driving means and has the advantageous features of simplified construction and low cost of production. This device, however, poses the problem that the amount of secondary air introduced therethrough tends to be insufficient, particularly in the case where the engine has a multiplicity of cylinders. In addition, this device cannot perform uniform secondary air distribution to all cylinders of the multi-cylinder engine.
It is, therefore, necessary to provide suitable countermeasures for overcoming these problems.
In the case where the multi-cylinder engine is mounted on a motorcycle, the engine and, accordingly, the exhaust gas cleaning system are exposed to the ambient air. It is desirable that the exhaust gas cleaning device be mounted in such a manner as to have minimum projection to the outside and be in close proximity to the existing equipment so as to minimize damage by external forces while not interfering with the attachment and maintenance of the existing equipment.
In the known exhaust gas cleaning device of the type mentioned above, the passage interconnecting the reed valve device and the exhaust system, i.e. the passage downstream from the reed valve device, acts not only as a passage for introducing the secondary air into the exhaust system but also as a passage for transmitting the pulsating exhaust pressure to the reed valve device to actuate the latter. Therefore, during the operation of the reed valve device, exhaust gas of high temperature is allowed to flow back momentarily into the above-mentioned passage to reach the reed valve device to heat the passage and the reed valve device. It is, therefore, necessary to take suitable measures for cooling the passage and the reed valve device.
In addition, when the reed valve device is mounted directly on the engine, the reed valve device is liable to be affected adversely by the heat generated in the engine to diminish its durability.
Furthermore, there is a problem of unfavorable noise generated by the reed valve device when it opens and closes repeatedly.